Modern vehicles are frequently provided with seat belts which can be pre-tensioned in the event of a collision or impending collision. The purpose of this pre-tensioning is to restrain the occupant in their seat so as to minimize acceleration of the occupant. This in turn minimizes the effect of the impact of the collision on the body.
Additionally vehicles may be provided with a selectable pre-tensioning mode which holds the seat occupant more firmly on demand. Such selectable pre-tensioning is provided, for example, upon selecting a vehicle “Sport” mode.
In known systems, pre-tensioning (both selectable and emergency) is achieved by actuating the belt itself, or one or more of the three seat belt fixing points, namely the inertia reel mount point, the B-pillar mount point and the buckle mount point. The inertia reel is mounted to the floor of the vehicle chassis and serves three purposes; firstly to hold the belt against the occupant's body in normal use, secondly to retrieve and coil up the seat belt when the belt is not in use, and thirdly to lock the belt in position in the event of an accident. The shoulder mount point is located towards the top of the B-pillar of the vehicle above the shoulder of the occupant. The buckle mount point is positioned inboard of the occupant's seat and is fixed to the vehicle floor.
Pre-tensioning is typically provided by either providing additional rotary input to the inertia reel or providing additional linear input to one of the attachment points or the belt itself. However, each of these solutions has associated problems.
Providing the inertia reel with additional rotary input is most commonly achieved using pneumatic power to provide the pre-tensioning rotation and a clutch to allow the reel to rotate independently of the pneumatic power during normal use. However it is necessary to provide gearing in order to generate the necessary force for activation. The gearing takes up additional space within the inertia reel due to the complexity of the mechanism. Furthermore, any increase in the diameter of the inertia reel increases the torque which the pre-tensioning mechanism must achieve in order to pre-tension the belt, which places a further burden on the gearing mechanism.
In the alternative, a linear input to the belt is technically simpler to achieve by provision of a linear pneumatic actuator. However such solutions only offer a limited pre-tensioning functionality, that pre-tensioning being limited by the length of the actuator stroke.
These problems are even more acute given the need for both selective and emergency actuation. It is an object of the present invention to at least mitigate some of the above problems.